David Sterba wrote on 2016/05/23 14:01 +0200:
The API does not seem right. It's fine to provide functions for full
int/u32/u64 ranges, but in the cases when we know the range from which
we request the random number, it has to be passed as parameter. Not
doing the % by hand.
This makes sense.
I'll add a new function to create random number for a given range.
+u32 rand_u32(void)
+{
+ struct timeval tv;
+ unsigned short rand_seed[3];
This could be made static (with thread local storage) so the state does
not get regenerated all the time. Possibly it could be initialize from
some true random source, not time or pid.
I also considered true random source like /dev/random, but since it's
possible to wait for entropy pool, it would be quite slow and confusing
for users.
So time with pid seems good enough.
+ long int ret;
+ int i;
+
+ gettimeofday(&tv, 0);
+ rand_seed[0] = getpid() ^ (tv.tv_sec & 0xFFFF);
+ rand_seed[1] = getppid() ^ (tv.tv_usec & 0xFFFF);
+ rand_seed[2] = (tv.tv_sec ^ tv.tv_usec) >> 16;
+
+ /* Crank the random number generator a few times */
+ gettimeofday(&tv, 0);
+ for (i = (tv.tv_sec ^ tv.tv_sec) ^ 0x1F; i > 0; i--)
+ nrand48(rand_seed);
This would be then unnecesssray, just draw the number from nrand.
Right, this part is just copied from libuuid, but in fact we don't
really need to be that random.
About patch separation: please introduce the new api in one patch, use
in another (ie. drop srand and switch to it).
OK, I'll update it in next version.
Thanks,
Qu
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